Research will be conducted with human volunteers to examine the self-administration, reinforcing effects and behavioral pharmacology of abused drugs. The primary set of experiments will explore the self-administration and reinforcing of drugs within a residential research laboratory with volunteers with histories of drug abuse. These studies will evaluate various clinically used anoretic-stimulant drugs (e.g., amphetamine, diethylpropion, chlorphentermine, fenfluramine) and sedative drugs (e.g., diazepam and pentobarbital). A second set of studies will provide additional information about anorectic-stimulant drugs by examining the effects of these compounds in normal outpatient volunteers. The particular emphasis of this set of studies will be on the interactive relationship between aorectic-stimulant drugs and human social behavior. A final set of studies will further extend the research on anorectic-stimulant drugs by systematically comparing the self-administration of these compounds in the therapeutic context of a treatment program for overweight. Overall, the results of these studies will contribute to improved understanding of and treatment procedures for nonopioid drug abuse.